Staff at the Salford plant of security packaging manufacturer API Holographics are threatening further industrial action after staging a 24-hour strike in a dispute over a pay freeze.

Members of the Unite union walked out yesterday after a breakdown in negotiations with the company.

According to the union, API Holographics, part of Cheshire-based API Group, is refusing to offer an "acceptable review" to existing staff under a pay neutral agreement, signed in 2009.

Employees agreed to the freeze when the company was in "some financial difficulties and making redundancies at the site", the union claimed.

It said that the company's fortunes have since turned around, which should trigger a clause in the agreement that would see the pay freeze scrapped.

The workers are also planning to continue an overtime ban.

Alison Jones, Unite regional officer, said: “The staff have always worked with their employer to ensure that it remains competitive, and have shown their willingness to compromise regarding previous wage claims.

“However, as the company has now returned to profit, they just wish to be rewarded for the commitment and support they have given, as these workers have not had a pay rise since 2007.”

API said it was disappointed by the action being taken by union members and that it had put in place measures to minimise the effect of the dispute on customers.

It said: “ Two years ago, at a time when API Holographics was in a very difficult trading position, the company offered a four-year pay freeze because we believed the alternative of a wage cut would be detrimental to employees.

“This was voted on and accepted by the workforce. This agreement allowed the company to plan its return to profitability and growth supported by stable wage costs . It is disappointing that, only two years into the agreement, just as the strategy is starting to bear fruit and allow us to consider further investment, some employees have decided to take this action.”

The strike action does not affect other API operations in the UK or abroad.